Pregnancy Weight Gain Calculator

Weight gain in pregnancy is normal and necessary. The extra weight is the baby, the placenta, amniotic fluid, extra blood volume, breast tissue and fat stored for breastfeeding. How much is recommended depends mainly on your body mass index before you conceived, which is why this calculator starts there rather than with a single figure for everyone.

For a woman who started at a healthy BMI, the widely used guidance from the Institute of Medicine is a total gain of about 11.5 to 16 kilograms, with roughly half a kilogram a week in the second and third trimesters. Women who started underweight are advised to gain more, around 12.5 to 18 kilograms. Those who started overweight are advised around 7 to 11.5 kilograms, and those in the obese range about 5 to 9 kilograms. Gaining less than the recommendation is associated with lower birth weight; gaining much more raises the risk of gestational diabetes, high blood pressure and a larger baby.

The pattern matters as much as the total. Most women gain only a small amount, sometimes nothing, in the first trimester because of nausea and appetite changes. The steady gains come from about week 14 onward, and the last few weeks often bring a further chunk from fluid and the growing baby. This calculator uses that shape, so the "typical gain by week" figure stays modest early and rises later.

Two notes. First, this is general guidance, not a personal prescription — twins, medical conditions and your clinician's assessment can all move the targets. Second, pregnancy is not the time for deliberate weight loss. If you are concerned about your weight or the pattern of your gain, raise it with your midwife or doctor rather than acting on a website.

This calculator returns estimates for general information only. It is not medical advice, diagnosis or treatment, and it cannot replace an assessment by a qualified health professional. Individual results vary, and figures such as calorie needs, body-fat percentage and heart-rate zones are approximations based on population averages rather than measurements of you.